In applications for fluid flow temperature control valves, as for example, heater core inlet control valves for controlling the flow of engine coolant to the passenger compartment heater, it is desirable to provide continuous bypass flow when the valve is closed in order that the temperature of the fluid at the valve inlet is maintained at the engine coolant ambient. However, where a bypass or branch channel is used at the temperature control valve inlet, a problem arises in preventing bypass flow when the temperature control valve is open and it is intended that all fluid entering the control valve inlet pass through the main flow passage of the valve and not be diverted to the bypass channel.
In automotive passenger compartment temperature control systems, it is known to provide a sensor for sensing the temperature of the air in the passenger compartment and couple the sensor to an actuator which modulates the position of the heater core coolant inlet valve to vary the amount of engine coolant entering the heater core thereby controlling the temperature of the fluid in the heater core. Since the engine coolant temperature is maintained at a fairly constant value by the engine thermostat during normal engine operation, the heater core coolant inlet valve can be modulated to vary the temperature of the heater core in response to the sensor and thus operated to maintain the temperature in the passenger compartment at a substantially constant desired value.
In the above-described automatic temperature control system, it is necessary that the temperature of the coolant at the inlet of the heater core temperature control valve be maintained substantially constant in order that the valve movement in response to the sensor signals will be able to provide changes in the heater core temperature sufficiently rapidly to compensate for changes in the temperature of the passenger compartment as determined by the sensor. If the fluid supply line to the heater inlet valve comprises a single line when the heater inlet valve is closed or nearly closed, the nearly static fluid in the line from the engine to the heater inlet valve is cooled by heat transfer to the hose or connecting tube and, thus, is not maintained at the desired inlet temperature to provide rapid temperature response of the heating system.
In addition, the fluid valve can serve as an engine thermostat bypass, thereby allowing elimination of the fixed bypass and, thus, provide more coolant flow for the heater core.
In order to provide a more rapid temperature change response in the heater, in response to sensor signals, it is desirable to use a bypass type inlet valve which permits a continuous flow of engine coolant past the inlet of the valve when the valve is closed or nearly closed. However, where such a bypass or branch flow arrangement is used at the valve inlet, when the valve opens, the supply line is feeding not only the main channel through the open valve but also the bypass or branch line and, thus, the main flow channel through the temperature control valve is robbed of sufficient flow of heated fluid, which in turn decreases the temperature response capability of the heater.
When a non-bypass automotive coolant valve is shut, back pressure in the output line from the water pump is increased to 50-90 psig (340-612 Kpa) thereby increasing the load on the engine required to drive the coolant pump. A bypass type coolant valve eliminates such an increase of engine loading when the valve is closed.
Alternatively, the temperature output of heaters is often modulated by varying the position of a blend air door, which blends fully heated air with unheated air from outside the vehicle in varying proportions, either manually or by means of a servoactuator. In these cases the valve is not used to modulate the coolant flow through the heater core but it is merely an on-off device.
Since coolant is always flowing through the inlet hose to a bypass type valve, devices such as temperature sensing emission controls can be connected to the heater valve line rather than tapped into the cooling jacket of the engine block, where such devices would be generally inaccessible and subjected to a more hostile environment.
Thus, it has been desired to find a technique for employing a bypass type temperature inlet valve in a fluid temperature control system and yet provide a device which utilizes only a single valve but yet limits flow to the bypass when the temperature inlet valve is open.